Method of delayed ignition in blasting



1966 G. M. PRATLEY 3,264,987

METHOD OF DELAYED IGNITION IN BLASTING Filed March 10, 1965 GEozQe Mon779G115. fiflney ,4- rpm.

Patented August 9, 1966 3,264,987 METHOD OF DELAYED IGNITION IN BLASTINGGeorge M. Pratley, Factoria, Luipaardsvlei, Transvaal, Republic of SouthAfrica, assignor to Pratley Igniters (Proprietary) Limited, Factoria,Luipaardsvlei, Transvaal, Republic of South Africa Filed Mar. 10, 1965,Ser. No. 438,529 4 Claims. (Cl. 10227) This invention relates to theignition of igniter cord or fuse as used in blasting operations andhereinafter termed a fuse; in a method of regulating the delay in suchignition, and in the apparatus for carrying out the method.

Obtaining the ignition of an igniter cord or a fuse by the use ofchemicals is well known and numerous chemicals have been used and theirreactions have been regulated by various means. In this specificationthe word fuse will be used for the ignition means between the igniterand the explosive.

It is the object of this invention to provide that the control of someprescribed time for the ignition of the fuse shall be regulatable by theparticular chemicals used and their careful preparation. Such chemicalsbeing used in the form of a solid mixture containing the essentialchemical substance or substances to which water is added as theactivating agent. It is a feature of this invention that in itsapplication no actively poisonous ingredients are used, nor are toxicgases generated.

According to this invention an igniter for a fuse comprises a holder forthe end of the fuse to bring it into heat contact with an anhydrousmetal oxide mixed with water repellent which on contact with water, formthe required regulatable time barrier to the hydration of the oxide toproduce the required heat.

According to this invention as an alternative to the water repellentmaterial, a water soluble ingredient is used or a mixture of both thewater soluble ingredients and the water repellent material.

Other features of the invention provide for the anhydrous metal oxide tobe unslaked lime in granular form mixed with the delay producingadditives and the mixture pressed to a suitable form.

The invention provides also for the delay producing additives to includesaccharides and metal salicylates together with metal stearates.

The invention also provides a container for the igniter consisting of anon-metallic cylinder with a lid, both impervious to water, said lidperforated with an aluminium tube, said tube closed at its end and inwhich the end of the fuse is crimped. With each igniter there issupplied a proper proportion of water in a sealed plastic bag.

There are several other ingredients both water soluble, and waterrepellents which could be used, with of course the necessary changes inthe mixture but the most suitable formula has been used to describe theinvention.

In carrying out the invention in one preferred manner, to a given weightof calcium oxide there is mixed two percent of its weight of sodiumsalicylate and a similar weight of magnesium stearate and also a similarweight of cane sugar. All these added materials are in dry powder formand are thoroughly mixed in the sequence above mentioned. They arecompressed as a block or made up into small pellets and placed in thecontainer above mentioned.

The amount of water required to make the mixture react effectively willbe approximately twenty-two and one half percent of the weight of thecalcium oxide.

Under normal conditions after the water is added there will be a delayof about one hour after which the fuse, buried in the wetted mixture,will be ignited through the chemical reaction taking place.

There are of course many other chemicals which may be used but the aboveprovides a typical example of what is required. By varying the amount ofthe water soluble ingredients in the case mentioned and the amount ofthe magnesium stearate water repellent, the time of ignition can bevaried as desired.

The figure shows an ignition package.

The package forming the igniter is illustrated in the accompanyingdrawing in which 1 shows a waterproof container closed by a cover 2,through which passes the tube 3. On assembly, the fuse 9 has its endplaced in the tube 3 and crimped therein. In the container 1 is theblock of heat producing material 5 the tube 3 therein is closed at itsbottom end 4 and at its top suitably attached to the cover 2. When theigniter is to be made active the plastic bag 6 of water 7 is puncturedand the water tipped into the container 1 and the cover 2 fastenedthereto. Vents 8 should be made to allow steam to escape under the cover2.

The igniter is now set and in due time, depending on the provisions madeas above described, the fuse will become ignited.

If the igniter is to be preserved in good condition until brought intouse it must be kept free from contact with moist air. For this purposean impervious bag 10 encloses the igniter and is sealed at both ends. Ifthe bag has been punctured it will collapse completely on beingsqueezed, if it is still sealed the igniter should be in good condition.11 is a wire bail to hold the cover from falling off the top ofcontainer 1.

What I claim as new and desire to secure by Letters Patent is:

1. An igniter for delayed ignition of a fuse comprising means forholding the end of said fuse in heat contact with a metal oxide, wellmixed with water soluble material and a water repellent, said mixtureproviding a time regulator for the hydration of said metal oxide when awater charge is added to the mixture.

. 2. A mixture for a fuse igniter consisting of unslaked lime and timedelaying additives comprising metallic salicylates, metallic stearatesand saccharides.

D 3. A mixture for a fuse igniter consisting of unslaked lime, 1.8percent of its weight of sodium salicylate and 2 percent of its weightof magnesium stearate and also 2.1 percent of its weight of cane sugar.

4. A non-metallic water proof container holding a mixture of materialsforming an igniter for delayed ignition of a fuse including a ventedcover into which an aluminium closed ended tube is secured to come intoheat contact with the mixture in said container, said container beingenclosed in a bag of moisture impervious material.

References Cited by the Examiner UNITED STATES PATENTS 255,042 3/1882Smith et al. 10223 273,399 3/1883 Schneebeli 10224 963,161 7/1910 Lilley10222 1,167,288 1/ 1916 Frensdorf 10227 BENJAMIN A. BORCHELT, PrimaryExaminer.

V. R. PENDEGRASS, Assistant Examiner.

1. AN IGNITER FOR DELAYED IGNITION OF A FUSE COMPRISING MEANS FORHOLDING THE END OF SAID FUSE IN HEAT CONTACT WITH A METAL OXIDE, WELLMIXED WITH WATER SOLUBLE MATERIAL AND A WATER REPELLENT, SAID MIXTUREPROVINDING A TIME